Semiconductor device and manufacturing method thereof

ABSTRACT

A method includes forming a semiconductor fin over a substrate; forming first, second, and third gate structures crossing the semiconductor fin; forming first source/drain epitaxy structures over the semiconductor fin and on opposite sides of the first gate structure and forming second source/drain epitaxy structures over the semiconductor fin and on opposite sides of the second gate structure, wherein bottom of the first source/drain epitaxy structures and bottom of the second source/drain epitaxy structures are lower than a top surface of the semiconductor fin; removing the third gate structure to expose the top surface of the semiconductor fin; forming an isolation structure in the semiconductor fin, wherein a bottom of the isolation structure is lower than the bottom of the first source/drain epitaxy structures and the bottom the second source/drain epitaxy structures.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a Divisional Application of U.S. application Ser. No. 15/628,728, filed Jun. 21, 2017, now U.S. Pat. No. 11,387,232, issued on Jul. 12, 2022, which claims priority to U.S. Provisional Application Ser. No. 62/475,330, filed Mar. 23, 2017, which are herein incorporated by references.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapid growth. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs.

Such scaling down has also increased the complexity of processing and manufacturing ICs and, for these advances to be realized, similar developments in IC processing and manufacturing are needed. For example, a three dimensional transistor, such as a fin-like field-effect transistor (FinFET), has been introduced to replace a planar transistor.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIGS. 1A to 1M are cross-sectional views of a method for manufacturing a semiconductor device at various stages in accordance with some embodiments of the present disclosure.

FIGS. 2A to 2B are cross-sectional views of a method for manufacturing a semiconductor device at various stages in accordance with some embodiments of the present disclosure.

FIGS. 3A to 3C are cross-sectional views of a method for manufacturing a semiconductor device at various stages in accordance with some embodiments of the present disclosure.

FIG. 4 is cross-sectional view of a semiconductor device in accordance with some embodiments of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

The present disclosure is directed to, but not otherwise limited to, a FinFET device. The FinFET device, for example, may be a complementary metal-oxide-semiconductor (CMOS) device comprising a P-type metal-oxide-semiconductor (PMOS) FinFET device and an N-type metal-oxide-semiconductor (NMOS) FinFET device. The following disclosure will continue with a FinFET example to illustrate various embodiments of the present invention. It is understood, however, that the application should not be limited to a particular type of device, except as specifically claimed.

FIGS. 1A to 1M are cross-sectional views of a method for manufacturing a semiconductor device at various stages in accordance with some embodiments of the present disclosure.

Reference is made to FIG. 1A. A substrate 100 is provided. The substrate 100 may be a bulk silicon substrate. Alternatively, the substrate 100 may include an elementary semiconductor, such as silicon (Si) or germanium (Ge) in a crystalline structure; a compound semiconductor, such as silicon germanium (SiGe), silicon carbide (SiC), gallium arsenic (GaAs), gallium phosphide (GaP), indium phosphide (InP), indium arsenide (InAs), and/or indium antimonide (InSb); or combinations thereof. Possible substrates 100 also include a silicon-on-insulator (SOI) substrate. SOI substrates are fabricated using separation by implantation of oxygen (SIMOX), wafer bonding, and/or other suitable methods.

Some exemplary substrate 100 also includes an insulator layer. The insulator layer includes suitable materials, including silicon oxide, sapphire, and/or combinations thereof. An exemplary insulator layer may be a buried oxide layer (BOX). The insulator is formed by one or more suitable process(es), such as implantation (e.g., SIMOX), oxidation, deposition, and/or other suitable process. In some exemplary semiconductor substrate 100, the insulator layer is a component (e.g., layer) of a silicon-on-insulator substrate.

The substrate 100 may also include various doped regions. The doped regions may be doped with p-type dopants, such as boron or BF₂; n-type dopants, such as phosphorus or arsenic; or combinations thereof. The doped regions may be formed directly on the substrate 100, in a P-well structure, in an N-well structure, in a dual-well structure, and/or using a raised structure. The substrate 100 may further include various active regions, such as regions configured for an N-type metal-oxide-semiconductor transistor device and regions configured for a P-type metal-oxide-semiconductor transistor device.

In some embodiments, the substrate 100 also includes a fin structure 110. The fin structure 110 may be patterned by any suitable method. For example, the fin structure 110 may be patterned using one or more photolithography processes, including double-patterning or multi-patterning processes. Generally, double-patterning or multi-patterning processes combine photolithography and self-aligned processes, allowing patterns to be created that have, for example, pitches smaller than what is otherwise obtainable using a single, direct photolithography process. For example, in one embodiment, a sacrificial layer is formed over a substrate and patterned using a photolithography process. Spacers are formed alongside the patterned sacrificial layer using a self-aligned process. The sacrificial layer is then removed, and the remaining spacers may then be used to pattern the fin structure 110.

A plurality of isolation structures 105 are formed on the substrate 100 and adjacent to the fin structure 110. The isolation structures 105, which act as a shallow trench isolation (STI) around the fin structure 110 may be formed by chemical vapor deposition (CVD) techniques using tetra-ethyl-ortho-silicate (TEOS) and oxygen as a precursor. In yet some other embodiments, the isolation structures 105 are insulator layers of a SOI wafer.

A gate dielectric 115, a dummy gate material layer 120, and a mask layer 131 are deposited sequentially on a substrate 100 by, for example, low pressure CVD (LPCVD) and plasma enhanced (PECVD).

A photo resist pattern (not shown) is coated on the mask layer 131 and is exposed and developed to form a desire pattern. The mask layer 131 is dry etched (such as plasma etching) in turn with the photo resist pattern as a mask, until the dummy gate material layer 120 is exposed. As a result, the patterned mask layer 131 is formed. The plasma etching gas may include gas containing halogen, for example, fluoro-gases such as fluorocarbon gas (C_(x)H_(y)F_(Z)), NF₃, SF₆, or other halogen-containing gases such as Cl₂, Br₂, HBr, HCl, or it may include oxidants such as oxygen, ozone and oxynitride. In some embodiments, after etching, wet cleaning is performing with de-ionized water and the like or dry cleaning is performing with oxygen, fluorinated gas and the like to completely remove the resultant of etching.

The gate dielectric 115 may be formed by thermal oxidation, chemical vapor deposition, sputtering, or other methods known and used in the art for forming a gate dielectric. The gate dielectric 115 may include, for example, a high-k dielectric material such as metal oxides, metal nitrides, metal silicates, transition metal-oxides, transition metal-nitrides, transition metal-silicates, oxynitrides of metals, metal aluminates, zirconium silicate, zirconium aluminate, or combinations thereof.

The dummy gate material layer 120 may include materials having different etching selectivity from the materials of the mask layer 131, such as polycrystalline silicon, amorphous silicon and/or microcrystal silicon. The mask layer 131, which is used as a hard mask layer during etching later, may include silicon oxide, silicon nitride and/or silicon oxynitride. In some embodiments, the dummy gate material layer 120 may include polycrystalline-silicon (poly-Si) or poly-crystalline silicon-germanium (poly-SiGe). Further, the dummy gate material layer 120 may be doped poly-silicon with uniform or non-uniform doping.

The mask layer 131, in some other embodiments, may include silicon nitride (SiN), silicon oxynitride (SiON), silicon carbide (SiC), SiOC, spin-on glass (SOG), a low-K film, tetraethylorthosilicate (TEOS), plasma enhanced CVD oxide (PE-oxide), high-aspect-ratio-process (HARP) formed oxide, amorphous carbon material, tetraethylorthosilicate (TEOS), other suitable materials, and/or combinations thereof.

Reference is made to FIG. 1B. A removing (or etch) process is then performed to remove portions other than the intended pattern of the dummy gate material layer 120 (see FIG. 1A) and the gate dielectric 115 to form a plurality of dummy gates 121, 122, and 123. The dummy gate 121 is adjacent to the dummy gate 122, and the dummy gate 122 is adjacent to the dummy gate 123, in which the dummy gate 122 is between the dummy gates 121 and 123. The dummy gates 121, 122, and 123 have gate lengths T1, T2, and T3, respectively, in which the gate lengths T1, T2, and T3 are substantially the same. That is, the dummy gates 121, 122, and 123 have substantially the same profiles (or shapes). The gate length T1, T2, and T3 are parallel to the direction extending from, for example, the dummy gate 121 to the dummy gate 122. A distance D1 between a first side 121A of the dummy gate 121 and the first side 122A of the dummy gate 122 is substantially equal to a distance D2 between a first side 122A of the dummy gate 122 and the first side 123A of the dummy gate 123. In other words, the distance D1 (or D2) is substantially equal to half of a distance D3 between a first side 121A of the dummy gate 121 and the first side 123A of the dummy gate 123. The distances D1 and D2 may also be referred to as gate pitches. From another perspective, a distance D11 between the dummy gates 121 and 122 is substantially equal to a distance D22 between the dummy gates 122 and 123. The term “substantially” as used herein may be applied to modify any quantitative representation which could permissibly vary without resulting in a change in the basic function to which it is related.

In some embodiments, the dummy gate material layer 120 and the gate dielectric 115 (see FIG. 1A) may be patterned by an etching process, such as a dry plasma etching process or a wet etching process. At least one parameter, such as etchant, etching temperature, etching solution concentration, etching pressure, source power, radio frequency (RF) bias voltage, etchant flow rate, of the patterning (or etching) recipe can be tuned. For example, the same or similar dry etching process used for etching the patterned mask layer 131 (see FIG. 1A), such as plasma etching, may be used to etch the dummy gate material layer 120 and the gate dielectric 115 until the fin structure 110 is exposed.

Reference is made to FIG. 1C. A plurality of gate spacers 140 are formed respectively on opposite sidewalls of the dummy gates 121, 122, and 123, the gate dielectric 115, and the mask layer 130. In some embodiments, at least one of the gate spacers 140 includes single or multiple layers. The gate spacers 140 can be formed by blanket depositing one or more dielectric layer(s) (not shown) on the previously formed structure. The dielectric layer(s) may include silicon nitride (SiN), oxynitride, silicon carbon (SiC), silicon oxynitride (SiON), oxide, and the like and may be formed by methods utilized to form such a layer, such as CVD, plasma enhanced CVD, sputter, and other methods known in the art. The gate spacers 140 may include different materials with different etch characteristics than the dummy gates 121, 122, and 123 so that the gate spacers 140 may be used as masks for the patterning of the dummy gates 121. The gate spacers 140 may then be patterned, such as by one or more etch(es) to remove the portions of the gate spacers 140 from the horizontal surfaces of the structure.

Reference is made to FIG. 1D. One or more recessing process(es) is(are) performed to the substrate 100 to form a plurality of recesses 112 in the fin structure 110 of the substrate 100. The fin structure 110 of the substrate 100 may be recessed by suitable process including dry etching process, wet etching process, and/or combination thereof. The recessing process may also include a selective wet etch or a selective dry etch. A wet etching solution includes a tetramethylammonium hydroxide (TMAH), a HF/HNO₃/CH₃COOH solution, or other suitable solution. The dry and wet etching processes have etching parameters that can be tuned, such as etchants used, etching temperature, etching solution concentration, etching pressure, source power, RF bias voltage, RF bias power, etchant flow rate, and other suitable parameters. For example, a wet etching solution may include NH4OH, KOH (potassium hydroxide), HF (hydrofluoric acid), TMAH (tetramethylammonium hydroxide), other suitable wet etching solutions, or combinations thereof. Dry etching processes include a biased plasma etching process that uses a chlorine-based chemistry. Other dry etchant gasses include CF₄, NF₃, SF₆, and He. Dry etching may also be performed anisotropically using such mechanisms as DRIE (deep reactive-ion etching).

Reference is made to FIG. 1E. A plurality of source/drain features 152 and 154 are respectively formed over the substrate 100 and in the recesses 112 (shown in FIG. 1D). In greater details, the source/drain features 152 are formed in the first region 182 of the substrate 100, and the source/drain features 154 are formed in the third region 186 of the substrate 100. At least one of the source/drain features 152 is formed between the dummy gates 121 and 122, and at least one of the source/drain features 154 is formed between the dummy gates 122 and 123.

In some embodiments, the source/drain features 152 and 154 may be epitaxy structures, and may also be referred to as epitaxy structures 152 and 154. The source/drain features 152 and 154 may be formed using one or more epitaxy or epitaxial (epi) processes, such that Si features, SiGe features, and/or other suitable features can be formed in a crystalline state on the fin structure 110. In some embodiments, lattice constants of the source/drain features 152 and 154 are different from lattice constants of the fin structure 110, and the source/drain features 152 and 154 are strained or stressed to enable carrier mobility of the semiconductor device and enhance the device performance. The source/drain features 152 and 154 may include semiconductor material such as germanium (Ge) or silicon (Si); or compound semiconductor materials, such as gallium arsenide (GaAs), aluminum gallium arsenide (AlGaAs), silicon germanium (SiGe), silicon carbide (SiC), or gallium arsenide phosphide (GaAsP).

In some embodiments, for a NMOS transistor, the source/drain features 152 and 154 may include SiP, SiC, SiPC, Si, III-V compound semiconductor materials, or combinations thereof for the n-type epitaxy structure. During the formation of the n-type epitaxy structure, n-type impurities such as phosphorous or arsenic may be doped with the proceeding of the epitaxy. For example, when the source/drain features 152 and 154 include SiC or Si, n-type impurities are doped. The epitaxy processes include CVD deposition techniques (e.g., vapor-phase epitaxy (VPE) and/or ultra-high vacuum CVD (UHV-CVD)), molecular beam epitaxy, and/or other suitable processes. The epitaxy process may use gaseous and/or liquid precursors, which interact with the composition of the fin structure 110 (e.g., silicon). Thus, a strained channel can be achieved to increase carrier mobility and enhance device performance. The source/drain features 152 and 154 may be in-situ doped. If the source/drain features 152 and 154 are not in-situ doped, a second implantation process (i.e., a junction implant process) is performed to dope the source/drain features 152 and 154. One or more annealing processes may be performed to activate the source/drain features 152 and 154. The annealing processes include rapid thermal annealing (RTA) and/or laser annealing processes.

Reference is made to FIG. 1F. After the source/drain features 152 and 154 are formed, an interlayer dielectric 170 is formed over the substrate 100 and at outer sides of the gate spacers 140. Accordingly, the interlayer dielectric 170 covers the source/drain features 152 and 154 and portions of the fin structure 110 of the substrate 100. The interlayer dielectric 170 may include silicon oxide, oxynitride or other suitable materials. The interlayer dielectric 170 includes a single layer or multiple layers. The interlayer dielectric 170 can be formed by a suitable technique, such as CVD or ALD. A chemical mechanical planarization (CMP) process may be applied to remove excessive interlayer dielectric 170. After the chemical mechanical planarization (CMP) process, the dummy gates 121, 122, and 123 are exposed from the interlayer dielectric 170.

Reference is made to FIG. 1G. A patterned hard mask (HM) 180 is formed over the fin structure 110 of the substrate 100. In some embodiments, the hard mask 180 is formed over the interlayer dielectric 170 and the dummy gates 121 and 123 to define a first region 182, a second region 184, and a third region 186. The hard mask 180 covers the first region 182 and the third region 186 and leaves the second region 184 being uncovered. In other words, the hard mask 180 exposes the dummy gate 122 (see FIG. 1F) in the second region 184, and the dummy gates 121 and 123 may be protected by the hard mask 180 during process(es) performed later.

The dummy gate 122 is removed to from a recess 114 in the second region 184. The recess 114 exposes portions of the fin structure 110 of the substrate 100 in the second region 184. In some embodiments, the dummy gate 122 is removed by a selective etch process, including a selective wet etch or a selective dry etch, and carries vertical profile of the gate spacers 140. With the selective etch process, the recess 114 is formed with a self-alignment nature, which relaxes process constrains, such as misalignment, and/or overlay issue in lithograph process, recess profile controlling in etch process, pattern loading effect, and etch process window.

Reference is made to FIG. 1H. A dielectric layer 190 is formed over the fin structure 110 of the substrate 100 and filling the recess 114 shown in FIG. 1G. In some embodiments, the dielectric layer 190 may include SiO₂, SiON, Si₃N₄, SiOCN, or combinations thereof. The dielectric layer 190 may be formed by a suitable technique, such as CVD, ALD and spin-on coating. Reference is made to FIG. 1I. A chemical mechanical planarization (CMP) process is performed to the dielectric layer 190 including the mask layer 180 shown in FIG. 1H to remove the excessive dielectric layer 190 and planarize the top surface of the second dielectric layer 190 with the dummy gates 121 and 123. After the CMP process, a dielectric structure 190′ is formed. In other words, the dummy gate 122 (see FIG. 1F) is replaced by the dielectric structure 190′.

Reference is made to FIG. 1J. A mask layer 200 is formed over the fin structure 110 of the substrate 100. The mask layer 200 is formed over the third region 186 and covers the dummy gate 123 to protect the dummy gate 123 during process(es) performed later. In other words, the dummy gate 121 (see FIG. 1I) in the first region 182 is exposed from the mask layer 200.

A replacement gate (RPG) process scheme is employed. In some embodiments, in a RPG process scheme, a dummy gate is formed first and is replaced later by a metal gate after high thermal budget processes are performed. Accordingly, the dummy gate 121 (see FIG. 1I) and the gate dielectric 115 are removed to from a recess 116 in the first region 182. The recess 116 exposes portions of the tin structures 110 of the substrate 100 in the first region 182. In some embodiments, the dummy gate 121 and the gate dielectric 115 are removed by a selective etch process, including a selective wet etch or a selective dry etch, and carries vertical profile of the gate spacers 140.

Reference is made to FIG. 1K. A first gate stack 210 is formed in the recess 116 shown in FIG. 1J. In other words, the dummy gate 121 and the gate dielectric 115 (see FIG. 1I) are replaced by the first gate stack 210. The first gate stack 210 includes an interfacial layer (not shown), a gate dielectric 212 formed over the interfacial layer, and a gate metal 214 formed over the gate dielectric 212. The gate dielectric 212, as used and described herein, includes dielectric materials having a high dielectric constant, for example, greater than that of thermal silicon oxide (˜3.9). The gate metal 214 may include a metal, metal alloy, and/or metal silicide.

In some embodiments, the gate metal 214 included in the first gate stack 210 may include a single layer or alternatively a multi-layer structure, such as various combinations of a metal layer with a work function to enhance the device performance (work function metal layer), liner layer, wetting layer, adhesion layer and a conductive layer of metal, metal alloy or metal silicide). For example, the gate metal 214 may be an n-type or p-type work function layer. Exemplary p-type work function metals include TIN, TaN, Ru, Mo, Al, WN, ZrSi₂, MoSi₂, TaSi₂, NiSi₂, WN, other suitable p-type work function materials, or combinations thereof. Exemplary n-type work function metals include Ti, Ag, TaAl, TaAlC, TiAlN, TaC, TaCN, TaSiN, Mn, Zr, other suitable n-type work function materials, or combinations thereof. The work function layer may include a plurality of layers. The work function layer(s) may be deposited by CVD, PVD, electro-plating and/or other suitable process. In some embodiments, the first gate stack 210 formed is a p-type metal gate including a p-type work function layer. In some embodiments, the capping layer included in the first gate stack 210 may include refractory metals and their nitrides (e.g. TiN, TaN, W2N, TiSiN, TaSiN). The cap layer may be deposited by PVD, CVD, Metal-organic chemical vapor deposition (MOCVD) and ALD. In some embodiments, the fill layer included in the first gate stack 210 may include tungsten (W). The metal layer may be deposited by ALD, PVD, CVD, or other suitable process.

In some embodiments, the interfacial layer may include a dielectric material such as silicon oxide (SiO₂), HfSiO, and/or silicon oxynitride (SiON). The interfacial layer may be formed by chemical oxidation, thermal oxidation, ALD, CVD, and/or other suitable method. The gate dielectric 212 may include a high-K dielectric layer such as hafnium oxide (HfO₂). Alternatively, the gate dielectric 212 may include other high-K dielectrics, such as TiO₂, HfZrO, Ta₂O₃, HfSiO₄, ZrO₂, ZrSiO₂, LaO, AlO, ZrO, TiO, Ta₂O₅, Y₂O₃, SrTiO₃ (STO), BaTiO₃ (BTO), BaZrO, HfZrO, HfLaO, HfSiO, LaSiO, AlSiO, HfTaO, HfTiO, (Ba,Sr)TiO₃ (BST), Al₂O₃, Si₃N₄, oxynitrides (SiON), combinations thereof, or other suitable material. The high-K gate dielectric 212 may be formed by ALD, PVD, CVD, oxidation, and/or other suitable methods.

Reference is made to FIG. 1L. After the first gate stack 210 is formed, the mask layer 200 (see FIG. 1K) is removed. Another mask layer 220 is formed over the fin structure 110 of the substrate 100. The mask layer 220 is formed over the first region 182 and covers the first gate stack 210 to protect the first gate stack 210 during process(es) performed later. In other words, the dummy gate 123 (see FIG. 1K) in the third region 186 is exposed from the mask layer 220.

A replacement gate (RPG) process scheme is employed to the dummy gate 123 (see FIG. 1K). Some relevant details of the replacement gate (RPG) process are similar to the processes described in FIGS. 1J to 1K, and, therefore, a description in this regard will not be repeated. After the replacement gate process, a second gate stack 230 is formed. In other words, the dummy gate 123 is replaced by the second gate stack 230. Similar to the first gate stack 210, the second gate stack 230 includes an interfacial layer (not shown), a gate dielectric 232 formed over the interfacial layer, and a gate metal 234 formed over the gate dielectric 232. The first gate stack 210 and the second gate stack 230 are active gates, and may also be referred to as first active gate 210 and the second first active gate 230.

The gate metal 234 of the second gate stack 230 is different from the gate metal 214 of the first gate stack 210 to define different threshold voltage (VT) region. That is, a metal component of the first gate stack 210 is different from a metal component of the second gate stack 230. As a result, the first region 182 and the third region 186 may also be referred to as a first VT region 182 and a second VT region 186, respectively. Moreover, the dielectric structure 190′ may act as an isolation structure to separated different VT regions. Accordingly, the second region 184 may be referred to as an isolation region 184, and the dielectric structure 190′ may also be referred to as an isolation structure 190′.

Reference is made to FIGS. 1B and 1L. The dummy gates 121, 122, and 123 are replaced respectively by the first gate stack 210, the dielectric structure 190, and the second gate stack 230. The first gate stack 210, the dielectric structure 190, and the second gate stack 230 are separated from each other.

Since the dummy gates 121, 122, and 123 have substantially the same profiles, the first gate stack 210, the dielectric structure 190, and the second gate stack 230 accordingly have substantially the same profiles (or shapes). As a result, the length T2 of the dielectric structure 190′ is substantially equal to the gate lengths T1 and T3 of the first gate stack 210 and the second gate stack 230. A distance D1 between a first side 210A of the first gate stack 210 and the first side 190A of the dielectric structure 190′ is substantially equal to a distance D2 between a first side 190A of the dielectric structure 190′ and the first side 230A of the second gate stack 230. In other words, the distance D1 (or D2) is substantially equal to half of a distance D3 between a first side 210A of the first gate stack 210 and the first side 230A of the second gate stack 230. The distances D1 and D2 may also be referred to as gate pitches. From another perspective, a distance D11 between the first gate stack 210 and the dielectric structure 190′ is substantially equal to a distance D22 between the dielectric structure 190′ and the second gate stack 230.

Reference is made to FIG. 1M. A plurality of conductive features 240 are formed in the interlayer dielectric 170 to form a semiconductor device 10. The conductive features 240 may be formed by recessed the interlayer dielectric 170 to form a plurality of openings (not shown) that expose the source/drain features 152 and 154. Metal such as tungsten is then deposited into the openings down to the source/drain features 152 and 154 to form conductive features 240 (not shown) in the interlayer dielectric 170.

At least one of the source/drain features 152 is disposed over the substrate 100 and between the first gate stack 210 and the dielectric structure 190′, and at least one of the source/drain features 154 is disposed over the substrate 100 and between the second gate stack 230 and the dielectric structure 190′. Moreover, a bottom surface 210S of the first gate stack 210, a bottom surface 230S of the second gate stack 230, and a bottom surface 192 of the dielectric structure 190′ are substantially coplanar.

FIGS. 2A to 2B are cross-sectional views of a method for manufacturing a semiconductor device at various stages in accordance with some embodiments of the present disclosure.

Reference is made to FIG. 2A. After the dummy gate 122 (see FIG. 1F) is removed, as described in FIG. 1G, an implantation process is then performed to the exposed portions of the fin structure 110 of the substrate 100. Thus, an implantation region 250 is formed in the fin structure 110. In some embodiments, the implanted ions of the implantation process may be, but not limited to, carbon, nitrogen, or oxygen. In some other embodiments, in the case of a p-type substrate 100 with p-wells, n-type ions such as phosphorous (P), arsenic (As) or antimony (Sb) may be implanted in the substrate 100. Similarly, in the case of an n-type substrate 100 with n-wells, p-type ions such as boron (B) may be implanted in the substrate 100.

Reference is made to FIG. 2B. Accordingly, the implantation region 250 is formed in the fin structure 110 of the substrate 100, and disposed under the dielectric structure 190′. The implantation region 250 is in contact with the dielectric structure 190′. Also the dummy gate 121 and 123 in FIG. 2A are replaced by gate stacks 210 and 230, respectively. The implantation region 250 and the dielectric structure 190′ are disposed in an isolation region 184 of the substrate 100, and may be collectively act as an isolation structure to isolate a first region 182 having a first gate stack 210 and a second VT region 186 having a second gate stack 230. In some embodiments, the first gate stack 210 and the second gate stack 230 have different metal components, as described in FIG. 1L. Other relevant structural details of the semiconductor device 10 of FIG. 2B are similar to the semiconductor device 10 of FIG. 1M, and, therefore, a description in this regard will not be repeated hereinafter.

FIGS. 3A to 3B are cross-sectional views of a method for manufacturing a semiconductor device at various stages in accordance with some embodiments of the present disclosure.

Reference is made to FIG. 3A. After the dummy gate 122 (see FIG. 1F) is removed, as described in FIG. 1G, a recessing process is performed to the exposed portions of the fin structure 110 of the substrate 100 to form a recess 118 in the fin structure 110 of the substrate 100. In some embodiments, the recess 118 may be tuned such that a depth D3 of the recess 118 in the substrate 100 is larger than a depth D4 of the epitaxy structures 152 and a depth D5 of the epitaxy structures 154. That is, the recess 118 is formed deeper than the epitaxy structures 152 and 154. However, in some other embodiments, the depth D3 may be smaller or substantially equal to the depth D4 and the depth D5.

Reference is made to FIG. 3B. An implantation process is performed to the exposed portions of the substrate 100 through the recess 118. Thus, an implantation region 252 is formed in the substrate 100. The implantation region 252 is similar to the implantation region 250 described in FIG. 2B, and similar details are omitted for simplicity. In some embodiments, a surface passivation process, an annealing process, or combinations thereof may also be performed to the substrate 100.

Reference is made to FIG. 3C. A dielectric structure 190′ is formed over the substrate 100 and filling the recess 118 (see FIG. 3B). Also the dummy gate 121 and 123 in FIG. 3B are replaced by gate stacks 210 and 230, respectively. That is, the dielectric structure 190′ is embedded in the substrate 100 (or the fin structure 110), and between the first gate stack 210 and the second gate stack 230. The implantation region 250 is disposed under a dielectric structure 190′. In greater details, the implantation region 250 is in contact with the dielectric structure 190′. The dielectric structure 190′ has a depth D3′ in the substrate 100, in which the depth D3′ is larger than the depth D4 of the epitaxy structures 152 and the depth D5 of the epitaxy structures 154. That is, the dielectric structure 190′ is formed deeper than the epitaxy structures 152 and 154. From other perspective, a bottom surface 190S of the dielectric structure 190′ is lower than a bottom surface 152S of the epitaxy structures 152 and a bottom surface 154S of the epitaxy structures 154. However, in some other embodiments, the bottom surface 190S may be higher or substantially equal to the bottom surface 152S and the bottom surface 154S.

FIG. 4 is cross-sectional view of a semiconductor device in accordance with some embodiments of the present disclosure. A dielectric structure 190′ may include a first dielectric 1901 and a second dielectric 1902 disposed on the first dielectric 1901. The first dielectric 1901 and a second dielectric 1902 may be made from different materials, and may be made from SiO₂, SiON, Si₃N₄, SiOCN, or combinations thereof. The dielectric structure 190′ of FIG. 4 may be made by, for example, forming the first dielectric 1901 in a recess 118 in a fin structure 110 of a substrate 100, and forming the second dielectric 1902 over the first dielectric 1901. In some other embodiments, the dielectric structure 190′ may be multi-layer structures including more than three dielectric layers.

According to the aforementioned embodiments, a dummy gate is replaced by a dielectric structure to isolate at least two gate stacks having different metal components. The formation of the dielectric structure may reduce the device scale, such as a distance between two active gates. With this configuration, the performance of the semiconductor device can be improved.

According to some embodiments, a method includes forming a semiconductor fin over a substrate; forming first, second, and third gate structures crossing the semiconductor fin; forming first source/drain epitaxy structures over the semiconductor fin and on opposite sides of the first gate structure and forming second source/drain epitaxy structures over the semiconductor fin and on opposite sides of the second gate structure, wherein bottom of the first epitaxy structures and bottom of the second epitaxy structures are lower than a top surface of the semiconductor fin; removing the third gate structure to expose the top surface of the semiconductor fin; forming an isolation structure in the semiconductor fin, wherein a bottom of the isolation structure is lower than the bottom of the first epitaxy structures and the bottom of the second epitaxy structures.

According to some embodiments, a method includes forming a semiconductor fin over a substrate; forming first, second, and third gate structures crossing the semiconductor fin; forming first spacers on opposite sidewalls of the first gate structure, second spacers on opposite sidewalls of the second gate structure, and third spacers on opposite sidewalls of the third gate structure; forming first epitaxy structures over the semiconductor fin and on opposite sides of the first gate structure and forming second epitaxy structures over the semiconductor fin and on opposite sides of the second gate structure; removing the third gate structure to form a trench between the third spacers to expose a portion of the semiconductor fin; etching the portion of the semiconductor fin exposed by the trench between the third spacers; and forming a dielectric structure filling an entirety of the trench between the third spacers.

According to some embodiments, a method includes forming a semiconductor fin over a substrate; forming first, second, and third gate structures crossing the semiconductor fin; forming first epitaxy structures over the semiconductor fin and on opposite sides of the first gate structure and forming second epitaxy structures over the semiconductor fin and on opposite sides of the second gate structure; removing the third gate structure to expose a portion of the semiconductor fin; performing an implantation process to form an implantation region in the exposed portion of the semiconductor fin; and forming a dielectric structure over the implantation region in the semiconductor fin.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A method, comprising: forming a semiconductor fin over a substrate; forming first, second, and third gate structures crossing the semiconductor fin; forming first epitaxy structures in the semiconductor fin and on opposite sides of the first gate structure, and forming second epitaxy structures in the semiconductor fin and on opposite sides of the second gate structure, wherein bottom of the first epitaxy structures and bottom of the second epitaxy structures are lower than a top surface of the semiconductor fin; removing the third gate structure to form a recess in the semiconductor fin; forming an isolation structure in the recess, wherein a bottom of the isolation structure is lower than the bottom of the first epitaxy structures and the bottom of the second epitaxy structures.
 2. The method of claim 1, wherein the isolation structure has a curved bottom from a cross-sectional view.
 3. The method of claim 1, further comprising forming shallow trench isolation structures laterally surrounding the semiconductor fin, wherein the bottom of the isolation structure is lower than top surfaces of the shallow trench isolation structures.
 4. The method of claim 1, further comprising forming an implantation region interfacing the bottom of the isolation structure.
 5. The method of claim 1, further comprising after forming the isolation structure, replacing the first and second gate structures with first and second metal gate structures, respectively.
 6. The method of claim 1, further comprising forming spacers on opposite sidewalls of the first, second, and third gate structures, wherein removing the third gate structure is performed to form a trench between a pair of the spacers, and the isolation structure is formed in contact with the pair of the spacers.
 7. The method of claim 1, wherein the isolation structure has a greater width variation below the top surface of the semiconductor fin than above the top surface of the semiconductor fin.
 8. The method of claim 1, wherein a width of the isolation structure above the top surface of the semiconductor fin is substantially equal to a width of the first and second gate structures.
 9. The method of claim 1, wherein the isolation structure is made of a single material.
 10. A method, comprising: forming a semiconductor fin over a substrate; forming first, second, and third gate structures crossing the semiconductor fin; forming first spacers on opposite sidewalls of the first gate structure, second spacers on opposite sidewalls of the second gate structure, and third spacers on opposite sidewalls of the third gate structure; forming first epitaxy structures in the semiconductor fin and on opposite sides of the first gate structure and forming second epitaxy structures in the semiconductor fin and on opposite sides of the second gate structure; removing the third gate structure to form a trench between the third spacers to expose a portion of the semiconductor fin; etching the portion of the semiconductor fin exposed by the trench between the third spacers; and forming a dielectric structure filling an entirety of the trench between the third spacers.
 11. The method of claim 10, further comprising after forming the dielectric structure, replacing the first and second gate structures with first and second metal gate structures, respectively.
 12. The method of claim 10, further comprising performing an implantation process to form an implantation region in a portion of the semiconductor fin directly below the trench between the third spacers.
 13. The method of claim 12, wherein the implantation region is lower than bottoms of the first and second epitaxy structures.
 14. The method of claim 10, further comprising performing a planarization process to the dielectric structure.
 15. A method, comprising: forming a semiconductor fin over a substrate; forming first, second, and third gate structures crossing the semiconductor fin; forming first epitaxy structures in the semiconductor fin and on opposite sides of the first gate structure and forming second epitaxy structures in the semiconductor fin and on opposite sides of the second gate structure; removing the third gate structure to expose a portion of the semiconductor fin; performing an implantation process to form an implantation region in the exposed portion of the semiconductor fin; and forming a dielectric structure over the implantation region in the semiconductor fin.
 16. The method of claim 15, further comprising: after forming the dielectric structure, replacing the first gate structure with a first metal gate structure; and after replacing the first gate structure with the first metal gate structure, replacing the second gate structure with a second metal gate structure, wherein the first and second gate structures have different compositions.
 17. The method of claim 15, further comprising forming first spacers on opposite sidewalls of the first gate structure, second spacers on opposite sidewalls of the second gate structure, and third spacers on opposite sidewalls of the third gate structure, wherein removing the third gate structure is performed to form a trench between the third spacers, and a widest width of the implantation region is substantially equal to a distance between the third spacers.
 18. The method of claim 15, wherein a bottom of the implantation region is higher than bottoms of the first and second epitaxy structures.
 19. The method of claim 15, wherein a height of the dielectric structure is substantially equal to heights of the first and second gate structures.
 20. The method of claim 15, wherein a top surface of the implantation region is level with a top surface of the semiconductor fin. 